Boreholes for hydrocarbon (oil and gas) production, as well as for other purposes, are usually drilled with a drill string that includes a tubular drill pipe having a drilling assembly which includes a drill bit attached to the bottom end thereof. The drill bit is rotated to shear or disintegrate material of the rock formation to drill the wellbore. Rotation of the drill bit is often achieved by rotation of the drill pipe, e.g., from a drilling platform at a wellhead. Instead, or in addition, at least part of the drill pipe is in some applications driven by a mud motor forming part of the drill string adjacent the drill bit.
Some elements of the drill string, however, may include non-rotating or rotationally static components that are not to rotate during operation with the driven, rotating drill pipe. Instead, such non-rotating components are to maintain a substantially constant rotational orientation relative to a formation through which the borehole extends. Rotary Steerable Systems (RSS), for example, often comprise a non-rotating housing or sleeve that may slide longitudinally along the borehole with the drill string, but is not to rotate with the drill string during directional drilling operations.
When drilling oil and gas wells for the exploration and production of hydrocarbons, it is often necessary to deviate the well from the vertical along a particular direction. This is called directional drilling. Directional drilling is used, among other purposes, for increasing the drainage of a particular well by, for example, forming deviated branch bores from a primary borehole. It is also useful in the marine environment, where a single offshore production platform can reach several hydrocarbon reservoirs using a number of deviated wells that spread out in any direction from the production platform.
In directional drilling operations that employ rotary steerable systems having a non-rotating housing, housing roll is undesired. The stationary housing or sleeve, within which the drill pipe or tubular of the drill string typically rotates, provides a reference for steering of the drill bit during directional drilling. Any deviation from the reference tends to deviate the drilling operation from a desired well path.
Rotational stasis of the non-rotating housing is often achieved by a rotational anchor mechanism that is mounted on the housing and is radially expandable to press against the borehole wall, transferring rotation-resistive torque from the formation to the housing.